Dawn dead in Ceres orbit, ran out of fuel Oct 2018

[marcus]

As of 11:30 PM pacific on 8 August, simview says altitude 1740 km
speed 169 m/s
270 km more to descend

EDIT: At 9:00 AM pacific on 9 August, altitude 1680 km and speed 170 m/s

 

[marcus]

Simview as of 11 am pacific on 11 August gives the altitude as 1600 km (which means 130 km more to descend) and the speed as 173 m/s.

Rayman's status update for 10 August said that the probe was instructed to simply coast for 23 hours starting sometime 9 August because its descent was getting ahead of schedule. They had allowed slack in case discrepancies developed and additional maneuver was required but descent went more smoothly than anticipated. Rather than advance the schedule which would have been very complicated---just to gain a day---they let Dawn coast with its ion engine off, to use up the slack.

Since we've turned a page I'll bring forward the schedule for to have it handy:

Orbit    dates      altitude(km)  pixelsize(m) res/HST  period  soccerball at
RC3    April 23–May 9    (13,600)    (1,300)    24     15 days    (3.0 meters)
Survey    June 6-30      (4,400)      (410)     73     3.1 days    (1.0 meters)
HAMO    Aug 17–Oct 23    (1,470)      (140)     217    19 hours    (33 cm)
LAMO Dec 15–end of mission (375)      (35)      850    5.5 hours    (8.5 cm)

LAMO (low altitude mapping orbit) is where gamma spectroscopy and thermal neutron detection will play a major role in discovering the chemical composition of Ceres surface material ("regolith").

Most recent Simview altitude was 993.37 miles translating to 1598.67 km, so FWIW just barely under 1600 km. Simview sometimes gets ahead of the official status report, but it has been doing rather well as a tracker, so I'd say worth consulting.

 

[marcus]

Also for convenient reference, since we turned a page, here are reminders of how gamma and neutron spectroscopy works, and the projected structure based on observed density, rotation and oblateness.

Nuclei hit by cosmic ray protons release fast neutrons. Nuclei hit by neutrons emit distinctive frequency gamma---so one can "hear" what types of atoms, what chemical elements, are in the regolith. Fast neutrons are slowed ("moderated") most effectively by repeated collision with hydrogen nuclei so the percentage of slow ("thermal") neutrons the probe detects, compared with fast neutrons, will indicate how much hydrogen is in the regolith. This will give a handle on the water content.

 

[marcus]

As of 10 pm pacific on 11 August, Simview gives the altitude as 1560 km, just 90 km from the HAMO target, and speed 175 m/s. At this rate Dawn will have to spend another day or two coasting with the engine off, just to keep from achieving HAMO ahead of schedule.

 

[marcus]

This is what HAMO (the next-to-final orbit) is supposed to look like. Simview indicates Dawn is already there. Officially Dawn is not expected to start mapping the planetino until 17 August. There was probably slack in the schedule which would now be awkward to compress.

You can see 1470 km altitude at speed 180 m/s which are the HAMO (high altitude mapping orbit) target parameters.
Update Simview now (9:15am pacific) gives altitude 913.26 miles and 402 mph figures, which translate:
slightly less than 1470 km and just under 180 m/s

Just checked again (as of 9:37am pacific) 912.67 and 402 which translate to 1469 km and 180 m/s
Simview shows the planetto rotating, so you can see the headlights coming around in this shot:

 

[marcus]

Mission director Marc Rayman made it official. http://dawn.jpl.nasa.gov/mission/status.html
==quote Dawn status update 13 Aug==

August 13, 2015 - Dawn Arrives in Third Mapping Orbit

Dawn completed the maneuvering to reach its third mapping orbit and stopped ion-thrusting this afternoon. This was a little ahead of schedule because the spiral descent went so well that some of the allocated thrusting time was not needed. Since July 14, the spacecraft has reduced its orbital altitude from 2,700 miles (4,400 kilometers) to approximately 915 miles (1,470 kilometers). The orbit period has correspondingly decreased from 3.1 days to 19 hours.

Dawn is scheduled to begin its new observations on Aug. 17 and continue for more than two months. First, however, the mission control team will measure the actual orbit parameters accurately and transmit them to the spacecraft
==endquote==

 

[marcus]

Dawn is taking pictures!
==quote Rayman's Dawn status update==

August 17, 2015 - Third Mapping Campaign to Begin Tonight

The mission control team has now provided Dawn with accurate knowledge of its orbit parameters. They have also completed transmitting all of the other information it needs and confirmed that the explorer is ready for its new Ceres mapping campaign.

Dawn has been pointing its main antenna to Earth since Aug. 13. Shortly after 9:00 pm PDT today it will start rotating to point its camera and other sensors at the landscape below and will begin taking pictures over the north pole less than an hour later.
==endquote==
If this mapping sequence goes like the previous two, the craft will take pictures (and IR spectral data etc) while on the day side, on the way from the Npole to Spole, and then rotate around and transmit the pictures and data while it is on the night side, returning back to Npole. Then it has to rotate around again to point its cameras etc back at the surface to start taking pictures on the next pass over the day side. Each orbit cycle takes about 19 hours. And she will be in this orbit (1460-1470 km altitude) for about 2 months. So that's a lot of cycles and a lot of pictures. Sort of 60*24/19 ≈ 76 rounds as a rough estimate.

 

[marcus]

New status update:
==quote http://dawn.jpl.nasa.gov/mission/status.html ==
August 21, 2015 - Dawn's New Mapping Phase Off to a Smooth Start

Dawn is performing flawlessly as it takes pictures and collects other data in its new orbit. The spacecraft 's view is now three times as sharp as in its previous mapping orbit, which concluded in June.

At this orbital altitude, it takes Dawn 11 days to photograph all of Ceres and transmit the data to Earth. The probe is scheduled to map Ceres six times over the next two months. The latest Dawn Journal includes a description of the plans for this phase of the exploration of Ceres.
==endquote==
As the update notes, Marc Rayman has just posted the Dawn Journal for August:
http://dawnblog.jpl.nasa.gov/2015/08/21/dawn-journal-august-21/

 

[marcus]

Parts of the August Journal struck me as so interesting that I decided to quote. This excerpt describes how Dawn will actually be taking 3D pictures of Ceres landscape by making successive passes with the camera aimed at different angles---not always straight down, sometimes off to the side in various directions to get perspective on the various mountains, planes, and craters.
==quote August Journal==
In its first mapping cycle, which is taking place now, the explorer aims its instruments straight down. For the second, it will keep the camera pointed a little bit back and to the left, making another full map but with a different perspective. For the third, it will look a little back and to the right. The fourth map will be viewing the scenery ahead and to the left. The fifth map will be of the terrain immediately ahead, and the sixth will be farther back than the third but not as far to the right.
==endquote==
Rayman also reminds us of the other sensors operating concurrently with the main camera:

==quote==

In addition to the stereo pictures and the many spectra (which reveal the nature of the minerals as well as the surface temperature), Dawn will use the color filters in its camera to record the sights in visible and infrared wavelengths.
...
...
The probe also will continue to acquire spectra both of neutrons and of gamma rays. It is unlikely to detect more than a whisper of neutrons from Ceres at this height, but the radiation coming from elsewhere in space now will serve as a useful calibration when it measures stronger nuclear emanations from one quarter the altitude starting in December, allowing scientists to inventory Ceres’ atomic constituents.

Precise measurements of Dawn’s radio signal will reveal more details of the dwarf planet’s gravitational field and hence the distribution of mass within. When the spacecraft is not aiming its main antenna at Earth, it will broadcast through one of its three auxiliary antennas, and the Deep Space Network will be listening (almost) continuously throughout the 84 orbits.
==endquote==

The idea of continuous monitoring a carrier signal (even though no data is being transmitted) is that temporary Doppler shifts show the craft momentarily speeding up and slowing down in its orbit as it approaches and passes over subsurface concentrations of mass.
Mapping irregular variations in subsurface density could give clues as to the planetino's interior composition and geological history.

 

[mfb]

No pictures yet :(.

 

[marcus]

First pictures from HAMO--the next-to-nearest orbit are being posted. Here are some samples:
http://dawn.jpl.nasa.gov/multimedia/images/image-detail.html?id=PIA19631
http://photojournal.jpl.nasa.gov/tiff/PIA19631.tif
http://photojournal.jpl.nasa.gov/tiff/PIA19632.tif
http://photojournal.jpl.nasa.gov/tiff/PIA19633.tif
http://photojournal.jpl.nasa.gov/jpeg/PIA19633.jpg

New status update from Marc Rayman:
August 24, 2015 - Mapping Proceeding Extremely Well

Today Dawn is making its ninth orbital passage over the illuminated side of Ceres since beginning its new mapping phase. The explorer needs 12 dayside passes (each lasting 9.5 hours, or half an orbit) to see all of Ceres. (This is explained further in the latest Dawn Journal.)

 

[OmCheeto]

I was very, very disappointed when I saw the image of the mountain yesterday.

Getting closer was supposed to take away the mysteries of the planet. I've been told that I have a very good imagination, but this image is too strange for me to even attempt a description of what I'm looking at.

 

[OmCheeto]

After 10 minutes of staring, I came up with the following thoughts:

If it weren't 4 miles high, I'd say we are looking at "frost heaving".
Googling shows similar features here on Earth called "Pingos".
Given the low gravity of Ceres, I'm going to stick to this answer.
Until of course, someone points out, that I'm an idiot.

 

[marcus]

I also found there was something confusing and unsatisfying about that image. Hard to imagine the physical process of formation.

Just saw your "pingo" link. Great connection! possible analog!
https://en.wikipedia.org/wiki/Pingo#Formation
==quote==
Hydrostatic (closed-system) pingos form as a result of hydrostatic pressure on water from permafrost, and commonly form in drained lakes or river channels. Permafrost rises to the drained body's former floor. Pore water is expelled in front of the rising permafrost, and the resulting pressure causes the frozen ground to rise and an ice core to form. The shape and size of a hydrostatic or closed system pingo is often similar to the body of water that it originated from. They can vary from symmetrical conical domes to asymmetric, elongate hills.
==endquote==

We've seen some elongate ridges. maybe they could be pingos too.

Om, your pointing out the pingo bump-up process makes the images we have considerably more interesting. Thanks!

 

[OmCheeto]

...
Om, your pointing out the pingo bump-up process makes the images we have considerably more interesting. Thanks!

I was actually expecting; "You were right, Om. You are an idiot".
But I'll take a compliment.

 

[marcus]

New status update out today:
==quote==

August 27, 2015 - Dawn Completes First Mapping Observations

Shortly before midnight last night, Dawn completed its twelfth revolution over the sunlit side of Ceres in this mapping phase. That concluded the observations required to make the first map.

The spacecraft is now pointing its main antenna to Earth and transmitting its precious results. It will continue sending pictures and other data until tomorrow night.

Dawn will begin its second mapping cycle at this altitude around 11:00 PM PDT on August 28. As explained in the Dawn Journal, throughout the second mapping observations, it will point its camera a little back and to the left, rather than straight down, providing provide stereo views from which scientists can construct 3-D views of the alien terrain.
==endquote==
Om, one of the problems with that picture of the mountain, for me (and possibly for you), stems from its being taken straight down smack on the tip of the cone. So we couldn't see any suggestion of the conical shape. There was nothing to suggest height or perspective.
This next mapping cycle will, Rayman says, be taken with the camera pointed back and to the side, so we will get something looking a bit more like a mountain.

And eventually, I guess after all six mapping cycles are completed, the straight down and the various slantwise views will be digitally merged to give a 3D map of the surface.

In line with what Rayman said in the update, the DSN site shows Madrid antenna #65 receiving (pictures probably) data from Dawn at the rate 125 thousand bits per second. He says that will continue until tomorrow evening and then the new mapping cycle will start 11PM pacific on 28 August.

When it's not transmitting data Dawn seems to keep up a steady low bit-rate signal of 10 bits per second, which seems to me to be about detecting variations in subsurface density (by doppler from changes in the orbital speed as the craft flies over concentrations of mass). It can do that with one of the smaller antennas, while the camera is aimed at the ground. We should be able to see the changeover from the high bit-rate to the low, tomorrow, when mapping is resumed.

 

[Dotini]

My guess is that the formation was either driven up from below or deposited from above from nearby material - perhaps from the crater just below it in this view. Beneath are views of vaguely similar structures on Mars and Earth.

Butte in the transition zone between the cratered uplands of western Arabia Terra and the low, northern plains of Mars, formerly known as "The Face on Mars". Image credit: NASA

Brandberg Massif, Namibia
Image Credit: NASA/USGS

 

[marcus]

Om mentioned "frost heaving" earlier. I was curious about the mechanism, and looked it up. It almost sounds as if under certain conditions ice is attractive to water that is ready to freeze in the sense that moisture will percolate up through certain types of soil in order to bond to already existing ice crystals. It is physically easier for water to freeze onto an existing ice crystal than in the absence of one--so water will in effect be drawn to an icy layer. The icy layer grows, forcing particles of soil apart, creating pressure.
http://www.concretenetwork.com/conc...ow_footings/frost_actions_and_foundations.htm
==quote==
How Frost Heave Works
The volume increase that occurs when water changes to ice was at first thought to be the cause of frost heave, but it is now recognized that the phenomenon known as ice segregation is the basic mechanism.

Water is drawn from unfrozen soil to the freezing zone where it attaches to form layers of ice, forcing soil particles apart and causing the soil surface to heave. Without physical restraint there is no apparent limit to the amount of heaving that may occur. (Movements in excess of 4 in. developing under basement floors in only three weeks have been recorded.)

Where restraint in the form of a building load is present, heaving pressures may or may not overcome the restraint, but they can be very high: 19 tons/sq ft has been measured, and a seven-story reinforced concrete frame building on a raft foundation was observed to heave more than 2 in.

A different form of frost action, called "adfreezing," occurs when soil freezes to the surface of a foundation. Heaving pressures developing at the base of the freezing zone are transmitted through the adfreezing bond to the foundation, producing uplift forces capable of appreciable vertical displacements. If constructed of concrete block a basement wall may fail under tension and part at a horizontal mortar joint near the depth of frost penetration.

Controlling Factors
For frost action to occur three basic conditions must be satisfied: the soil must be frost-susceptible; water must be available in sufficient quantities; and cooling conditions must cause soil and water to freeze. If one of these conditions can be eliminated, frost heaving will not occur.

Frost-susceptibility is related to size distribution of soil particles. In general, coarse-grained soils such as sands and gravels do not heave, whereas clays, silts and very fine sands will support the growth of ice lenses even when present in small proportions in coarse soils. If frost-susceptible soils located where they will affect foundations can be removed and replaced by coarser material, frost heaving will not occur.

Water must be available in the unfrozen soil for movement to the freezing plane where the growth of ice lenses occurs. A high groundwater table with respect to the location of the ice lenses will therefore favour frost action...
==endquote==

 

[marcus]

Earlier Om called attention to the ice-driven mount called "pingo"
https://en.wikipedia.org/wiki/Pingo

Notice that on Earth, in the arctic, pingos get as high as 70 meters (230 ft)

How high does that suggest pingos could get on Ceres, under favorable conditions? The gravity is about 1/30 Earth's or about 3%.

I believe to have a pingo you need a subsurface water table, at least part of the time. there needs to be a subsurface thaw at least now and then, to provide liquid water which can be drawn into the freeze zone. Maybe someone else can explain the process of pingo-formation and estimate how it might go in low gravity. Favorable conditions would probably be extremely rare.

 

[johnnymorales]

After 10 minutes of staring, I came up with the following thoughts:

If it weren't 4 miles high, I'd say we are looking at "frost heaving".
Googling shows similar features here on Earth called "Pingos".
Given the low gravity of Ceres, I'm going to stick to this answer.
Until of course, someone points out, that I'm an idiot.

I had that same thought a few days ago when I first saw the picture, and made the comment that it looked like a pingo albeit it much larger than one on Earth on the article about the new pictures on phys.org. I imagine that without the restraints of gravity they'd be able to get much larger. Also since it's colder near the surface of Ceres ice should be a bit harder and able to maintain a large shape which it can't do on Earth.

Also if the internals of Ceres are just starting to freeze up (assuming therefore there is a liquid layer) according to one astronomer Mike Brown, the slow freezing of a deep liquid layer will eventually result in cyrovolcanoes,because ice expands as it freezes. As the layer of frozen water grows the pressure on th remaining liquid or slushy layer grows until the frozen layer gives and cracks allowing the liquid to escape upwards, and if there is enough pressure erupt as a cryovolcano.

Another thing to consider is this could be a parellel of what happens on Earth when mineral rich ground water flows for a long period. Over time dolomite or similar minerals are laid down rather quickly creating a steeply inclined hill (like in Yellowstone or Turkey).

On ceres with no atmospheric pressure, the water would quickly fizz away and maybe build a much steeper mineral deposit with much sharper edges since the water would barely flow downhill before it evaporated completely.

It would likely build so fast that at intervals it would partially collapse only be built up again as long as the water kept flowing.

Taking all those things together, ice could build a much larger structure on Ceres like we see.

 

[marcus]

Earlier Om called attention to the ice-driven mount called "pingo"
https://en.wikipedia.org/wiki/Pingo

Notice that on Earth, in the arctic, pingos get as high as 70 meters (230 ft)

How high does that suggest pingos could get on Ceres, under favorable conditions? The gravity is about 1/30 Earth's or about 3%.

I believe to have a pingo you need a subsurface water table, at least part of the time. there needs to be a subsurface thaw at least now and then, to provide liquid water which can be drawn into the freeze zone. Maybe someone else can explain the process of pingo-formation and estimate how it might go in low gravity. Favorable conditions would probably be extremely rare.

Since no one else has shown the arithmetic (although several of us seem to like the frost-heaving/pingo idea) I'll do it.

As a rough order of magnitude if pingos can get 70 meters high in Earth gravity, then in 1/30 gee
where the overburden weighs 1/30
and with the same physics producing the upthrust pressure
we can just multiply 70 x 30 and get 2100 meters
or 2 kilometers, which is order of magnitude right for the height of the mountain.

the same balance of forces which on Earth makes a pingo 70 meters would make a pingo of 2 kilometers on Ceres. Close enough to be suggestive.
We can only guess what other factors (lower temperature, longer lifespan, sources of additional subsurface hydraulic pressure, type of soil) could have contributed to raising that mountain 3 times higher, to 6 kilometers.

 

[marcus]

I think the transmission of pictures and data from the first HAMO cycle is nearly complete. DSN https://eyes.nasa.gov/dsn/dsn.html shows Goldstone #24 still receiving at 125 kilobit per second, but that should be over by 11 PM.
There are to be 6 cycles. The second one starts around 11 PM pacific this evening. We should see a 10 bits per second tracking signal then, at DSN, instead of the 125 kilobits per second data transmission signal from DAWN's main antenna.

 

[marcus]

Yes, the second mapping cycle must have started about then:
==quote Rayman status update 31 Aug==
August 31, 2015 - Dawn's Second Mapping Cycle Underway

Orbiting Ceres at an average altitude of 915 miles (1,470 kilometers), Dawn is photographing the dwarf planet for a new map. Each map requires observations during 12 flights over the dayside of Ceres (plus two more while it transmits the pictures and spectra to Earth). The team calls this one "cycle." (See the August Dawn Journal for more on how the mapping works.)

Today the spacecraft is making its fourth flight over the dayside of Ceres in the second mapping cycle.
==endquote==
I'll bring forward the schedule for to have it handy:

Orbit    dates      altitude(km)  pixelsize(m) res/HST  period  soccerball at
RC3    April 23–May 9    (13,600)    (1,300)    24     15 days    (3.0 meters)
Survey    June 6-30      (4,400)      (410)     73     3.1 days    (1.0 meters)
HAMO    Aug 17–Oct 23    (1,470)      (140)     217    19 hours    (33 cm)
LAMO Dec 15–end of mission (375)      (35)      850    5.5 hours    (8.5 cm)

LAMO (low altitude mapping orbit) is where gamma spectroscopy and thermal neutron detection will play a major role in discovering the chemical composition of Ceres surface material ("regolith").

Rayman says Dawn is completing 4 orbits today. 4 passes over the day side, taking pictures.
Just to check, 4 x 19 = 76, divided by 24 is a little over 3. A little over 3 days. The second cycle got started about 3 days ago late Friday evening. Now it's late afternoon Monday, three days... It makes sense.

Simview shows Dawn JUST having passed over the S pole and over to the night side, so it may be a little out of sync but not too bad. DSN shows Dawn still TAKING pictures because just sending a secondary tracking signal 10 bits per second, from one of the small antennas. Or maybe just finished taking pictures and in the process of turning around to transmit data.

http://dawn.jpl.nasa.gov/mission/status.html
https://eyes.nasa.gov/dsn/dsn.html
http://neo.jpl.nasa.gov/orbits/fullview2.jpg

 

[OmCheeto]

I posted my "pingo" hypothesis on Dawn's Facebook page, and a student living in Alessandria, Italy, liked my idea.
I checked out his Facebook page, and he posted a pictures of a pingo in Canada, and "The lonely mountain" on Ceres.
Eerily similar in appearance:

I traced his Canadian image to a website: Planetary Geomorphology Image of the Month, based in the UK.
The article was titled: Closed (hydrostatic) pingos on Earth and possibly Mars

Favorable conditions would probably be extremely rare.

Well, there is only one mountain on Ceres. I would call that "rare".

But here is the new problem.
How far can I go with my nutty theories?
PF has a policy of "No personal theories".
But, we seem to be looking at a Trekkian/PF dichotomous problem, as "No man, has gone here, before".

Meh...
As always, I'll take the plunge, and state that it may be the crater to the lonely mountain's south, that is the engine generating the lift.
The "seed" of the mountain may be a long lost comet, possibly billions of years old. I've heard that comets are very light.

------------
Ok2di&b

 

[marcus]

I wouldn't call that a personal theory so much as a reasonable conjecture within the framework of the common body of physics.
That's a really neat find
https://planetarygeomorphology.word...c-pingos-on-earth-and-possibly-mars/#more-445
from the online "Planetary Geomorphology"

You are right that only one mountain on Ceres would be "rare". But maybe we will eventually see more---maybe smaller, maybe not so perfectly round.
Pingos can sometimes be oblong.

Something had to provide the heat and it is rather late in the day for internal radioactive decay. You are conjecturing that it could have been a comet that crashed into Ceres and formed the nearby crater.
This strikes me as good thinking and I bet we will eventually see some cautious professional thinking along just these lines!

==============
One thing they may be waiting for is the 3D pictures of Lonely Mountain. Based on a few more mapping cycles, taking pictures of the same mountain from different angles. Then if it walks and quacks like a Pingo it will be respectable for serious people to suggest that it might be one. I am forced to chuckle a bit about the extreme caution being displayed.

The caption in your article said one of the Earth pingos was 48 meters high. the corresponding height in 1/30 gravity would be 1440 meters, I guess.

Can you understand their description of pingo formation?

 

[OmCheeto]

...You are conjecturing that it could have been a comet that crashed into Ceres and formed the nearby crater.

Not really. What would the the slowest case impact be on Ceres? Is it the same as escape velocity? That's around 1100 mph.
I was thinking more on the line of an ancient comet, sitting below the crust, and serendipitously having a deep crater created next to it, eons later.

It's my conjecture that the surfaces of craters are similar to parabolic reflecting ovens.
A flat surface absorbing sunlight would radiate much more of it's energy away, than a crater, which would thermally radiate back onto it's own walls,

So my imagination says that the area around a deep crater would be slightly warmer than a flat surface.
And if there weren't some type of "seed" object, I would imagine that pingos would form uniformly around the crater, rather than in just one spot.
Also, Mt. Lonely is very near the equator: 11° S.
So it would be an ideal location for maximal heating and cooling.

This strikes me as good thinking and I bet we will eventually see some cautious professional thinking along just these lines!

==============
One thing they may be waiting for is the 3D pictures of Lonely Mountain. Based on a few more mapping cycles, taking pictures of the same mountain from different angles. Then if it walks and quacks like a Pingo it will be respectable for serious people to suggest that it might be one. I am forced to chuckle a bit about this one.

It was just a random idea.

 

[mfb]

A flat surface absorbing sunlight would radiate much more of it's energy away, than a crater, which would thermally radiate back onto it's own walls,

It also has more surface for infrared emission. In thermal equilibrium those effects cancel each other exactly. It's the same reason why the shape of a black body does not matter for its temperature.

The effect of day/night differences (non-equilibrium situation) can be different.

 

[OmCheeto]

It also has more surface for infrared emission. In thermal equilibrium those effects cancel each other exactly. It's the same reason why the shape of a black body does not matter for its temperature.

The effect of day/night differences (non-equilibrium situation) can be different.

I was thinking more in the line of a black body cavity. Once a photon gets in, it's a bit harder for the thermal emissions to get out. Not sure about the thermodynamics of a crater though.
I got the idea from the pits spitting out jets from Churyumov-Gerasimenko.

ps. I'm just throwing out ideas. Everyone, please feel free to point out my misconceptions!

 

[mfb]

Once a photon gets in, it's a bit harder for the thermal emissions to get out.

You can increase the timescale until it reaches equilibrium, but you cannot change the equilibrium temperature. Sure, Ceres as a whole is not in perfect equilibrium, but it is quite close as primordial heat and nuclear decays shouldn't play such an important role today.

 

[marcus]

Status update from Rayman today:
==quote==
September 4, 2015 - Second Mapping Cycle Going Smoothly

Today Dawn is making its ninth transit over the illuminated hemisphere of Ceres in its second mapping cycle. Throughout this cycle, it is taking pictures and making spectral measurements of the terrain behind and to its left as it orbits the dwarf planet.

The spacecraft will complete its observations for this second map shortly before 1:00 a.m. PDT on Sept. 7. It will then spend almost two days (about 2.5 revolutions around Ceres) transmitting its results to NASA's Deep Space Network.
==endquote==
Each mapping cycle takes 12 passes over the day side of the planetto. Each orbit takes 19 hours, so 57 hours more to make the 3 remaining passes or about 2 Earth days 9 hours. Subtract that from 1am 7 Sept and you get 4pm on 4 Sept. Seems about right. The pass he was talking about must have concluded around 4pm today.

BTW if they had extra hydrazine, or could use the reaction wheels they could do more turning and do more of the broadcasting of pictures to Earth during the dead time on the NIGHT SIDE. But I think to conserve hydrazine they are SAVING UP more data from each mapping cycle and sending the whole saved-up batch at the end of the cycle, which adds the 2.5 days Rayman spoke of.

Got to respect the resourcefulness of the planners/navigators---how they find ways to stretch the scarce resources and get the job done. Even if it takes a little longer.

Looking forward to December when they finally get close enough to use gamma and neutron spectroscopy to savor the CHEMISTRY of Ceres surface dirt.

 

[mfb]

No pictures of the bright spots from HAMO orbit so far :(.

 

[Zeno Ether]

I processed the last image of the bright spots from NASA and got this:
https://twitter.com/gaasmosfet/status/640833712058449920
A strange square covering part of the largest spot. Weird.

 

[mfb]

Where do you see a square?
And where is the original image?

 

[Zeno Ether]

 

[Zeno Ether]

And the Original

original